1. Field of Invention
The invention relates to membrane keyboards/keypads and more particularly to a membrane keyboard/keypad having an arrangement for uniformly lighting keys from background.
2. Description of Related Art
Membrane keyboard/keypads are widely employed by notebook computers and cellular phones. Membrane keyboard/keypads are advantageous for being thin, lightweight, and compact. However, most types of notebook computers and cellular phones are limited to operate in a bright environment only since there is no backlight device provided.
For overcoming above drawback, many prior keyboard/keypad patents with backlight arrangement are disclosed. For example, Taiwanese Utility Model Patent No. M306,689 discloses a keyboard with backlight arrangement. However, in practice it is found that keys distal the LED (light-emitting diode) based backlight arrangement are not sufficiently illuminated. That is, keys are not illuminated uniformly.
The invention described later is an outgrowth of earlier work by the inventor hereof, described in U.S. Pat. No. 6,545,232. The patent, entitled “Thin light permeable keyboard multiple switch assembly including scissors type actuator mechanisms”, discloses a thin type light permeable keyboard including keys, bridge structures, a frame board, a luminescence board, a film circuit board, and a base board. Each light permeable key has a top face coated with a light permeable substrate layer, a light impermeable coating layer, and a light permeable protection layer. Each bridge structure is pivoted between each key and the frame board. The luminescence board mounted between the frame board and the film circuit board functions as a luminous member mated with the light permeable frame board, elastic members and keys to indicate the sculptured characters, symbols, numbers or patterns on the keys, thereby facilitating the user to operate the computer in a dark environment. The teachings of the patent are incorporated herein by reference.
The patent has been successfully used in a commercial application. However, in practice it is found that light emitted from the electrically powered luminescence board passing the light permeable frame board and the keys are not sufficiently lit to uniformly illuminate characters, symbols or patterns on the keys. Thus, the need for improvement still exists.